Methods of making paper tissue, towel, and the like, are well known, including various features such as Yankee drying, through-air drying (TAD), fabric creping, dry creping, wet creping, and so forth. Wet pressing processes have certain advantages over through-air drying (TAD) processes including: (1) lower energy costs associated with the mechanical removal of water rather than transpiration drying with hot air, and (2) higher production speeds, which are more readily achieved with processes that utilize wet pressing to form a web. See, Klerelid et al., Advantage™ NTT™: low energy, high quality, pages 49-52, Tissue World, October/November, 2008. On the other hand, through-air drying processes have become the method of choice for new capital investment, particularly, for the production of soft, bulky, premium quality towel products.
U.S. Pat. No. 7,435,312 to Lindsay et al. suggests a method of making a through-air dried product including rush-transferring the web followed by structuring the web on a deflection member and applying a latex binder. The patent also suggests a variation in basis weight between dome and network areas in the sheet. See col. 28, lines 55+. U.S. Pat. No. 5,098,522 to Smurkoski et al. describes a deflection member or belt with holes therethrough for making a textured web structure. The backside, or machine side of the belt has an irregular, textured surface that is reported to reduce fiber accumulation on equipment during manufacturing. U.S. Pat. No. 4,528,239 to Trokhan discusses a through-air dry process using a deflection fabric with deflection conduits to produce an absorbent sheet with a domed structure. The deflection member is made using photopolymer lithography. U.S. Patent Application Publication No. 2006/0088696 suggests a fibrous sheet that includes domed areas and cross machine direction (CD) knuckles having a product of caliper and a CD modulus of at least 10,000. The sheet is prepared by forming the sheet on a wire, transferring the sheet to a deflection member, throughdrying the sheet and imprinting the sheet on a Yankee dryer. The nascent web is dewatered by noncompressive means; See ¶156, page 10. U.S. Patent Application Publication No. 2007/0137814 of Gao describes a throughdrying process for making an absorbent sheet that includes rush-transferring a web to a transfer fabric and transferring the web to a through drying fabric with raised portions. The throughdrying fabric may be travelling at the same or a different speed than that of the transfer fabric. See ¶39. Note also U.S. Patent Application Publication No. 2006/0088696 of Manifold et al.
Fabric creping has also been referred to in connection with papermaking processes that include mechanical or compactive dewatering of the paper web as a means to influence product properties. See, U.S. Pat. No. 5,314,584 to Grinnell et al.; No. 4,689,119 and No. 4,551,199 to Weldon; No. 4,849,054 to Klowak; and No. 6,287,426 to Edwards et al. In many cases, operation of fabric creping processes has been hampered by the difficulty of effectively transferring a web of high or intermediate consistency to a dryer. Further patents relating to fabric creping include the following: No. 4,834,838; No. 4,482,429 as well as No. 4,448,638. Note also, U.S. Pat. No. 6,350,349 to Hermans et al. which discloses wet transfer of a web from a rotating transfer surface to a fabric. See also U.S. Patent Application Publication No. 2008/0135195 of Hermans et al., now U.S. Pat. No. 7,785,443, which discloses an additive resin composition that can be used in a fabric crepe process to increase strength. Note FIG. 7. U.S. Patent Application Publication No. 2008/0156450 of Klerelid et al., now U.S. Pat. No. 7,811,418, discloses a papermaking process with a wet press nip followed by transfer to a belt with microdepressions followed by downstream transfer to a structuring fabric.
In connection with papermaking processes, fabric molding as a means to provide texture and bulk is reported in the literature. U.S. Pat. No. 5,073,235 to Trokhan discloses a process for making absorbent sheet using a photopolymer belt which is stabilized by application of anti-oxidants to the belt. The web is reported to have a networked, domed structure that may have a variation in basis weight. See Col. 17, lines 48+ and FIG. 1E. There is seen in U.S. Pat. No. 6,610,173 to Lindsay et al. a method of imprinting a paper web during a wet pressing event that results in asymmetrical protrusions corresponding to the deflection conduits of a deflection member. The '173 patent reports that a differential velocity transfer during a pressing event serves to improve the molding and imprinting of a web with a deflection member. The tissue webs produced are reported as having particular sets of physical and geometrical properties, such as a pattern densified network and a repeating pattern of protrusions having asymmetrical structures. U.S. Pat. No. 6,998,017 to Lindsay et al. discloses a method of imprinting a paper web by pressing the web with a deflection member onto a Yankee dryer and/or by wet-pressing the web from a forming fabric onto the deflection member. The deflection member may be formed by laser-drilling the terephthalate copolymer (PETG) sheet and affixing the sheet to a throughdrying fabric. See Example 1, Col. 44. The sheet is reported to have asymmetric domes in some embodiments. Note FIGS. 3A and 3B.
U.S. Pat. No. 6,660,362 to Lindsay et al. enumerates various constructions of deflection members for imprinting tissue. In a typical construction, a patterned photopolymer is utilized. See Col. 19, line 39 through Col. 31, line 27. With respect to wet-molding of a web using textured fabrics, see also, the following U.S. Pat. Nos. 6,017,417 and 5,672,248 both to Wendt et al.; No. 5,505,818 to Hermans et al. and No. 4,637,859 to Trokhan. U.S. Pat. No. 7,320,743 to Freidbauer et al. discloses a wet-press process using a patterned absorbent papermaking felt with raised projections for imparting texture to a web while pressing the web onto a Yankee dryer. The process is reported to decrease tensiles. See Col. 7. With respect to the use of fabrics used to impart texture to a mostly dry sheet, see U.S. Pat. No. 6,585,855 to Drew et al., as well as U.S. Patent Application Publication No. 2003/0000664, now U.S. Pat. No. 6,607,638.
U.S. Pat. No. 5,503,715 to Trokhan et al. refers to a cellulosic fibrous structure having multiple regions distinguished from one another by basis weight. The structure is reported as having an essentially continuous higher basis weight network, and discrete regions of lower basis weight that circumscribe discrete regions of intermediate basis weight. The cellulosic fibers forming the low basis weight regions may be radially oriented relative to the centers of the regions. The paper is described as being formed by using a forming belt having zones with different flow resistances. The basis weight of a region of the paper is said to be generally inversely proportional to the flow resistance of the zone of the forming belt, upon which such a region was formed. See also, U.S. Pat. No. 7,387,706 to Herman et al. A similar structure is reported in U.S. Pat. No. 5,935,381, also to Trokhan et al., where the use of different fiber types is described. See also U.S. Pat. No. 6,136,146 to Phan et al. Also noteworthy in this regard is U.S. Pat. No. 5,211,815 to Ramasubramanian et al. which discloses a wet-press process for making absorbent sheet using a layered forming fabric with pockets. The product is reported to have high bulk and fiber alignment where many fiber segments or fiber ends are “on end” and substantially parallel to one another within the pockets forming on the sheet, which are interconnected with a network region substantially in the plane of the sheet. See also, U.S. Pat. No. 5,098,519 to Ramasubramanian et al.
Through-air dried (TAD), creped products are also disclosed in the following patents: U.S. Pat. No. 3,994,771 to Morgan, Jr. et al.; U.S. Pat. No. 4,102,737 to Morton; U.S. Pat. No. 4,440,597 to Wells et al. and U.S. Pat. No. 4,529,480 to Trokhan. The processes described in these patents comprise, very generally, forming a web on a foraminous support, thermally pre-drying the web, applying the web to a Yankee dryer with a nip defined, in part, by an impression fabric, and creping the product from the Yankee dryer. Transfer to the Yankee typically takes place at web consistencies of from about 60% to about 70%. A relatively uniformly permeable web is typically required.
Through-air dried products tend to provide desirable product attributes such as enhanced bulk and softness; however, thermal dewatering with hot air tends to be energy intensive and requires a relatively uniformly permeable substrate, necessitating the use of virgin fiber or virgin equivalent recycle fiber. More cost effective, environmentally preferred and readily available recycle furnishes with elevated fines content, for example, tend to be far less suitable for throughdry processes. Thus, wet-press operations wherein the webs are mechanically dewatered are preferable from an energy perspective and are more readily applied to furnishes containing recycle fiber which tends to form webs with permeability which is usually lower and less uniform than webs formed with virgin fiber. A Yankee dryer can be more easily employed because a web is transferred thereto at consistencies of 30% or so which enables the web to be firmly adhered for drying. In one proposed method of improving wet-pressed products, U.S. Patent Application Publication No. 2005/0268274 of Beuther et al. discloses an air-laid web combined with a wet-laid web. This layering is reported to increase softness, but would no doubt be expensive and difficult to operate efficiently.
Despite the many advances in the art, improvements in absorbent sheet qualities such as bulk, softness and tensile strength generally involve compromising one property in order to gain advantage in another or involve prohibitive expense and/or operating difficulty. Moreover, existing premium products generally use limited amounts of recycle fiber or none at all, despite the fact that the use of recycle fiber is beneficial to the environment and is much less expensive as compared with virgin kraft fiber.